Binoculars may be strapped onto a user's head or may hang from his neck in order to permit hands-free operation. The binoculars may be mounted on a mask which can be readily put on and taken off the user's head. When such a mask is employed for use in starlight and moonlight, the mask serves the additional purpose of precluding stray light from striking the eyes. The interconnection between the binoculars and the mask usually is such as to enable the binoculars to be readily movable between use and storage positions.
In order that a user can "wear" such binoculars or goggles, as they are sometimes called, with a minimum of discomfort, they should be lightweight. Of course, they should cost as little as possible without sacrificing performance.
Furthermore, the optical elements and image intensification devices used in such binoculars are expensive and subject to damage in the presence of water or even moisture. Thus, a waterproof construction is desirable, yet not achieved by binoculars heretofore available.
Such binoculars must have the capability of being focusable on a particular object and also of being adjustable to match the distance between the user's eyes.
In the past, such focusability and adjustability were afforded at the expense of water repellency. For Example, a device made by Baird-Atomic, Inc. of Bedford, Massachusetts had means to make adjustments in the interpupillary distance, but it was not waterproof. Thus, water could undesirably leak into the binoculars and damage the interior elements.
Waterproof devices such as shown in U.S. Pat. No. 3,787,688 to Stone have separate viewing elements for each eye which are not focusable nor are the optical elements desirably contained in a single housing.
A common approach to varying the interpupillary distance is disclosed in U.S. Pat. No. 3,454,773 to Bulthuis et al. in which the optical elements are respectively mounted in two wings 5 and 6 which are pivotable about a common axis. Sealing such a construction against moisture is not easily accomplished. The eyepieces being located externally to the housing renders it extremely difficult to seal them against moisture.